Fig. 1. Trail direction ratio (TDR; see text) as a function of temperature at ant height (4 mm) in a foraging trail of a Messor pergandei colony. Filled circles: data from E-day; Landers earthquake and subsequent aftershocks. The earthquake struck at the lowest temperature (05:58 h, 28 June, 1992). Temperature is a primary determinant of ant behavior, and also serves to separate data points in time; higher temperatures correspond to later times on all days. Other symbols: control days, all recordings starting at approximately the same time as on E-day. Empty squares, 29 June 1992; filled squares, 2 July 1992; crosses, 3 July 1992. Testing the null hypothesis by ANCOVA (slopes equal) yielded P>0.2. The common slope is 0.0142. Testing the null hypothesis (intercepts equal) yielded P>0.15. The common intercept is 0.138. The regression line for E-day is third from the top.